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19 Apr 2016, 11:03
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shivakumarmakka
Dear shivakumarmakka
I'm happy to respond.
Let's say
A = black earthworm population
B = red-brown earthworm population
Before event, A < B. Technically, A = 5B, approximately.
BUT, be careful. After event, it does not say A > B or even A = B. The exact wording is
"The population of black earthworms is now almost equal to that of the red-brown earthworm ..."
Technically, A is still less than B: now, not five times less, but just slightly less. It's misreading the question to say that A is greater than B.
Also, notice that nowhere in the question itself does it suggest that the black worms have increased. The prompt argument doesn't even contain the word "increase." In fact, the question is about B decreasing. The factory has blackened the woods, and presumably the black worms are now well camouflaged, but the red-brown worms are easier to spot, so the birds snack on these. We don't know whether the black worms have stayed the same or increases, but through some combination of B dropping and A staying the same or rising, A has almost caught up to B.
My friend, you have to remember that GMAT CR is as precise as mathematics. You have to look at every single word incredibly carefully. It appears you got the gist of the argument and concluded in your own mind that it was saying things different from what it actually says. Be very careful. As in any argument in the business world, the fine print matters, and many business deals that look great on the surface turn out to be nightmares when you examine the details.
Does all this make sense?
Mike
22 Oct 2018, 14:56
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TGC
okay here is my reasoning why i chose C
Since, in 1990, a factory was built in Millerton and emissions from the factory blackened much of the woods.
The population of black earthworms is now almost equal to that of the red-brown earthworm, i.e. the population of black worms increased and the population of brown worms stagnated
Local ecologists say it is the blackening of the woods.
Ecologists`s claim implies that emissions enabled black worms to use their color as a comouflage.
To strengthen this claim one need to find a factor that could have negative affect on black worms. so based on option (C) despite favourble conditions for the red brown worm, its population didn`t grow whereas for black worm though climate conditions were less favourable, their black camouflage gave them opprtunity for survival and growth in black woods. hence C
Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.
14 May 2019, 09:42
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A and B are good answers, but C is better.
A strengthens the argument because it says the red worm population is falling. One possible explanation is the black worms are now better camouflaged so the birds are eating more red worms.
But A isn’t ideal because there are other plausible explanations. Maybe there is a disease that’s killing red worms. We don’t know. A is tempting us to assume that the blackening of the forest is why the red worm population is falling but we don’t really know that for sure. So maybe this fact strengthens, or maybe it’s just a coincidence.
B is good, too, but it isn’t perfect. It says birds prefer black worms so you you would expect them to eat more black worms. Yet, the black worm population is rising. So we’re tempted to assume the birds would rather eat black worms but they aren’t doing so because the black worms aren’t visible so the birds settle for eating red. Okay, maybe. Or maybe the birds are still eating tons of black worms. We know the population of red and black is now equal but we don’t know that there are more black worms. Maybe they’re equal entirely because the population of red worms fell. Is that because the birds can see the red worms and are eating more of them? That’s a fair supposition but maybe something else, like disease or climate change, is causing the red worm population to fall.
And that takes us to C. C is best because it is ruling out these alternative explanations. A and B are plausible explanations, but they leave other possibilities open. C forecloses those possibilities.
This one is really hard, I would not fault anyone for picking A or B. We see a lot of questions where all the answers are bad and we have to find the least bad. Here, we have to pick the best of three pretty good answers.
Posted from my mobile device
A strengthens the argument because it says the red worm population is falling. One possible explanation is the black worms are now better camouflaged so the birds are eating more red worms.
But A isn’t ideal because there are other plausible explanations. Maybe there is a disease that’s killing red worms. We don’t know. A is tempting us to assume that the blackening of the forest is why the red worm population is falling but we don’t really know that for sure. So maybe this fact strengthens, or maybe it’s just a coincidence.
B is good, too, but it isn’t perfect. It says birds prefer black worms so you you would expect them to eat more black worms. Yet, the black worm population is rising. So we’re tempted to assume the birds would rather eat black worms but they aren’t doing so because the black worms aren’t visible so the birds settle for eating red. Okay, maybe. Or maybe the birds are still eating tons of black worms. We know the population of red and black is now equal but we don’t know that there are more black worms. Maybe they’re equal entirely because the population of red worms fell. Is that because the birds can see the red worms and are eating more of them? That’s a fair supposition but maybe something else, like disease or climate change, is causing the red worm population to fall.
And that takes us to C. C is best because it is ruling out these alternative explanations. A and B are plausible explanations, but they leave other possibilities open. C forecloses those possibilities.
This one is really hard, I would not fault anyone for picking A or B. We see a lot of questions where all the answers are bad and we have to find the least bad. Here, we have to pick the best of three pretty good answers.
Posted from my mobile device
